1. Field of the Invention
The present invention relates to a spread illuminating apparatus, and more particularly to a spread illuminating apparatus used with a liquid crystal display.
2. Description of the Related Art
A liquid crystal display (hereinafter referred to as LCD), which is small in power consumption, low in profile, and light in weight, is heavily used in electric products such as a personal computer (hereinafter referred to as PC), a cellular phone, and the like, and is increasingly demanded.
Since a liquid crystal of the LCD does not emit light by itself, the LCD requires an illuminating means to radiate light on the liquid crystal when used in a place where sunlight or interior lighting is not fully available.
A PC, particularly notebook-type PC, and a cellular phone are required to be lower in profile and smaller in power consumption, and the requirements are fulfilled by a spread illuminating apparatus of side light type, an example of which is shown in FIG. 10 (disclosed in Japanese Patent Application Laid-open No. 2000-11723).
In FIG. 10, a spread illuminating apparatus 1 is disposed over a front shoe F (upper side of the figure) of a reflection-type liquid crystal element 2. The spread illuminating apparatus 1 comprises: a light conductive plate 3 shaped substantially rectangular and made of a light transmissible material; a light conductive bar made of a light transmissible material; and spot-like light sources 5, 5 such as light emitting diodes (LEDs).
The light conductive plate 3 has a major surface 6 (upper aide in the figure, hereinafter referred to as xe2x80x9ctop surfacexe2x80x9d) which is an observing surface, and another major surface 7 (hereinafter referred to as xe2x80x9cbottom surfacexe2x80x9d) which faces the reflection-type liquid crystal element 2.
The light conductive bar 4 is disposed with its side surface 8 positioned close to or in contact with an end surface 9 of the light conductive plate 3, and has the light sources 5, 5 disposed on its both end surfaces 10, 10, respectively. The light conductive bar has an optical path conversion means 12 formed on its side surface 11 opposite to the side surface 8 facing the end surface 9 of the light conductive plate 3. The optical path conversion means 12 comprises a plurality of grooves 13 substantially triangular in section and a plurality of flat portions 14 present between adjacent grooves 13, 13, and is adapted to guide light rays emitted from the light sources 5, 5 toward the end surface 9 of the light conductive plate 3.
The light conductive plate 3 has a light reflection pattern 15 formed on the top surface 6. The light reflection pattern 15 comprises a plurality of grooves 16 shaped substantially triangular in section and extending parallel to the end surface 9 of the light conductive plate 3 and a plurality of flat portions present between adjacent grooves 16, 16, and is adapted to reflect light rays exiting out from the light conductive bar 4 toward the bottom surface 7.
In the spread illuminating apparatus 1 thus structured, light rays emitted from the light sources 5, 5 and introduced into the light conductive bar 4 have their optical paths changed at the optical path conversion means 12, and travel into the light conducive plate 3 through the end surface 9.
The light rays introduced into the light conductive plate 3 repeat reflections and reflections at the light reflection pattern 15 and other portions, progress toward an end surface opposite to the end surface 9, and exit out in the meantime from the bottom surface 7 to illuminate the reflection-type liquid crystal element 2 disposed close to the bottom surface 7, whereby the reflection-type liquid crystal element 2 performs emission (indirect emission) display function.
In the above described spread illuminating apparatus 1, the light rays emitted from the light sources 5, 5 are consumed while traveling inside the light conductive bar 4, and have their amounts decreased. To overcome this problem, a spread illuminating apparatus was disclosed in Japanese Patent Application Laid-open No. 2001-35222.
The spread illuminating apparatus disclosed therein is shown in FIG. 11. A light entry face 21 is provided at a corner 18 of a light conductive plate 3 so as to be substantially orthogonal to a line 20 (hereinafter referred to as xe2x80x9cdiagonal linexe2x80x9d) defined by connecting the corner 18 and a corner 19 diagonally opposite to the corner 18. A spot-like light source 5, for example an LED, is disposed close to or in contact with the light entry face 21. A light reflection pattern 15A is formed on a top surface of the light conductive plate 3. The light reflection pattern 15A comprises a plurality of arced grooves 16A and a plurality of flat portions 17A present between adjacent grooves 16A, 16A. The arced grooves 16A correspond to partial circumferences of circles which are concentric with one another about the light source 15 and which have respective different radii. Since this spread illuminating apparatus eliminates the light conductive bar 4 used in the apparatus shown in FIG. 10, light rays emitted from the light source 5 are introduced immediately into the light conductive palate 8, thereby preventing the loss of light conventionally incurred due to light traveling inside the light conductive bar 4.
Light rays are desired to exit out from the light conductive plates 3 in a uniform manner so as to ensure excellent illumination precision. For example, in the spread illuminating apparatus 1 disclosed in the aforementioned Japanese Patent Application Laid-open No. 2000-11723 (see FIG. 10), the grooves 16 of the light reflection pattern 15 have their depths increasing and/or have their in-between intervals decreasing with an increase in the distance from the light conductive bar 4. With this structure, light rays are reflected at the light refection pattern 15 toward the bottom surface 17 in a larger amount at a portion farther from the light conductive bar 14, whereby uniform emission is ensured all over the light conductive plate 3.
This is the case with the apparatus shown in FIG. 11, and the arced grooves 16A have their depths increasing and/or have their in-between intervals decreasing with an increase in the distance from the light source 5 in order to ensure uniform emission all over the light conductive plate 3. In this case, however, as shown in FIG. 12, the brightness decreases from an area positioned at and near the diagonal line 20 (hereinafter referred to as xe2x80x9cdiagonal line areaxe2x80x9d) toward an area positioned circumferentially away from the diagonal line area, specifically the brightness decreases with an increase in the emission angle xcfx86 made by the light direction line with respect to the diagonal line 20. This happens because the LED as the light source 5 has a light emission characteristic shown in FIG. 12, where with a datum luminous intensity defined by the luminous intensity of an LED whose emission angle xcfx86 of a direction along the paper surface of FIG. 11 (Xxe2x80x94X direction in FIG. 12) is 0xc2x0 and whose emission angle (referred to also as xe2x80x9cxcfx86xe2x80x9d for the sake of convenience) of a direction orthogonal to the paper surface of FIG. 11 (Yxe2x80x94Y direction in FIG. 12) is 0xc2x0, the ratio of the luminous intensity (relative luminosity) of the LED at a prescribed emission angle xcfx86 (Xxe2x80x94X direction or Yxe2x80x94Y direction) to the datum luminosity intensity is taken along the ordinate and shown as a function of the emission angle xcfx86 taken along the abscissa. As shown in FIG. 12, the relative luminosity decreases gradually as indicated by the solid line while the emission angle xcfx86 (Xxe2x80x94X direction) increases from 0xc2x0, hence the area corresponding to a larger emission angle xcfx86 has a lower luminous intensity in the spread illuminating apparatus shown in FIG. 11.
The present invention has been made in the light of the above, and it is an object of the present invention to provide a spread illuminating apparatus which ensures prevention of loss of light and improvement of illuminating precision
In order to achieve the object, according to a first aspect of the present invention, the spread illuminating apparatus comprises: a light conductive plate shaped substantially rectangular and made of a light transmissible material; a spot-like light source disposed close to or in contact with a light entry face provided at a corner of the light conductive plate; and a light reflection pattern which is formed on a major surface of the light conductive plate, comprises a plurality of arced grooves corresponding to circumferences of circles being concentric with one another about the light source and having respective different radii, and which is configured such that the depths of the arced grooves increase with an increase in a distance from the light source, and/or such that the intervals between adjacent arced grooves decrease with an increase in a distance from the light source, while each of the arced grooves has its depth increasing continuously and gradually with an increase in a distance from a line orthogonal to the light entry face.
According to a second aspect of the present invention, in the spread illuminating apparatus of the first aspect, each of the arced grooves has its depth determined according to an angle made by the line orthogonal to the light entry face with respect to a line defined by connecting a point concerned and the light source.
According to a third aspect of the present invention, in the spread illuminating apparatus of the first or second aspect, the light reflection pattern further comprises a plurality of flat portions each present between any two adjacent ones of the arced grooves.
According to a fourth aspect of the present invention, in the spread illuminating apparatus of the first or second aspect, the light reflection pattern is configured such that the plurality of arced grooves are continuously arrayed.
According to a fifth aspect of the present invention, in the spread illuminating apparatus of any one of the first to fourth aspects, the plurality of arced grooves are shaped substantially triangular in section.
The spread illuminating apparatus according to the present invention eliminates the light conductive bar conventionally used, whereby light rays emitted from the light source are introduced directly into the light conductive plate, thus preventing the loss of light conventionally incurred due to light traveling inside the light conductive bar. Further, the light reflection pattern of the spread illuminating apparatus is structured such that not only the grooves have their depths increasing with an increase in the distance from the light source but also each of the grooves has its depth increasing continuously and gradually with an increase in the distance from the diagonal line, whereby the light reflection pattern reflects more light toward the front surface of the reflection-type liquid crystal element at an area positioned far from the light source and the diagonal line than at an area positioned at or close to the light source and the diagonal line, thus achieving further uniform spread emission all the way over the light conductive plate, resulting in improvement of illuminating precision.